To avoid problems related to the liquid phase, solid sorbents functionalized with
ammine have been developed using a wide variety of different supports with the development of different types of nanomaterials and artificial nanostructures with a high surface area; several types of nanostructured substrates were used to increase specific surfaces and thus C[O.sub.2] absorption rate.
Furthermore, ammonia can generate a large amount of zinc
ammine complexes immediately in the solution and these complexes are absorbed on the six side planes of ZnO nanorods, which can facilitate the growth of ZnO nanorods structure by slowing down the growth velocity of the side surfaces [30].
To overcome the difficulties with liquid ammonia precursors, also solid reductants have been proposed, as for example, ammonium salts and metal
ammines [5].